The present invention concerns a filter device for mass exchange between two media separated by a membrane and an end cap for such a filter device.
Such filter devices are generally used as dialyzers, hemofilters or ultrafilters. The filter devices generally consist of a casing in the form of a tubular section with end caps in its end areas. A tubular fiber bundle which functions as a membrane is usually arranged in the casing so that a reliable seal is provided between the first flow space formed by the fiber cavities and a second flow space surrounding the membrane on the outside.
One problem with the design of the inflow and/or outflow chambers connected to the first flow space, i.e., to the hollow fiber bundle, is how to distribute the liquid so that it is apportioned evenly to the individual fibers of the hollow fiber bundle, and so that dead zones in the distribution of liquid are avoided.
There are known dialyzers where the inlet of the chambers connected to the hollow fiber bundle is arranged axially, with the axis of the flow channel running approximately through the mid point of the hollow fiber bundle. This generally yields the disadvantage that use of the fibers varies greatly, and at the same time there are areas where the flow velocity is approximately zero (dead zones). After finishing a dialysis treatment, such dead zones are the areas where the patient""s blood remains behind. In addition, there is a great difference between the flow velocity in the inlet and that in the fibers. The blood is exposed to a stress situation due to the resulting velocity gradient.
Unexamined German Patent DE-OS 26 46 358 describes a filter device where the end caps have a tangential inlet and the blood is carried in a channel in circulation through the ends of the hollow fibers. Blood flows tangentially through the hollow fiber ends. To achieve the most uniform possible distribution of liquid, only the areas of the casting compound in overflow circulation are provided with hollow fibers, while the rest of the core area does not have any fibers. This achieves uniform loading of the fibers but also results in a relatively low capacity or suboptimal utilization of the filter device on the whole due to the lack of hollow fibers at the center of the casing. To achieve a uniform rate of circulation of blood in the channel, the cross-sectional area of the channel in one embodiment decreases in the direction of flow.
It has also been proposed that the inlet be located parallel to the plane of the fiber ends and that the medium should change directions by 90 degrees in the end area of the inlet. Due to the small amount of available space and the manufacturing restrictions due to the injection molding process, only an abrupt change of directions is possible in general, but that would constitute a considerable burden on the blood.
The object of the present invention is to improve upon a generic filter device so that the transfer of blood from the inlet into the fibers is accomplished at a low load and the fibers are loaded uniformly.
This object is achieved according to the present invention by a filter device whose membrane is designed in the form of a hollow fiber bundle, its fiber cavities forming a first flow space, with at least one inflow or outflow chamber which communicates with the first flow space being provided for supplying a medium to the hollow fiber bundle or removing a medium from it, said chamber being adjacent to an essentially circular or semicircular channel which communicates with an inlet or outlet of the filter device and is designed to be open in the direction of the ends of the hollow fibers, said channel being arranged approximately centrally with the hollow fiber bundle, having a cross-sectional area that decreases in the direction of flow and having an outside diameter smaller than the diameter of the hollow fiber bundle. This yields, first, the advantage that the blood flow undergoes only relatively gentle and low-stress changes in direction and velocity of flow. With the device according to the present invention, the flow velocity in the path through the essentially circular or semicircular channel gradually approaches the value of the velocity inside the fibers with the device according to the present invention.
Second, this yields the advantage that the blood is distributed in a pattern having approximate radial symmetry due to the changing cross-sectional area along the path through the channel. This means that approximately the same amount of blood flow leaves the channel and flows outward radially in each angular area. This yields a uniform utilization of the individual fibers of the hollow fiber bundle and thus yields optimum utilization of fiber capacity.
In contrast with the previously known solutions to this problem, there is no marked turbulence with the arrangement according to the present invention, but instead the distribution of the fluid or the blood has a mainly uniform radial symmetry.
It is especially advantageous if the end areas of the hollow fibers are held in a casting compound which extends parallel to the channel. The casting compound is usually, designed in the form of disks; with the ends of the hollow fibers being arranged in a uniform distribution in the casting compound.
According to a preferred embodiment of the present invention, the height and/or width of the channel decreases in the direction of flow. It is especially advantageous if the cross-sectional area of the channel decreases linearly with the flow path. Such a design yields the result that identical quantities of liquid or blood are discharged from the channel per angle area, thus resulting in a distribution that has approximate radial symmetry.
It is especially advantageous if there is an inlet or outlet extending radially, developing into the channel according to the present invention in its one end area and forming the mouth of a connection of the filter device in its other end area.
The diameter of the circular or semicircular channel may advantageously be 2 to 4 times, preferably 2.5 to 3.5 times, the diameter of the inlet or outlet.
In another embodiment of the present invention, the diameter of the circular or semicircular channel may be less than {fraction (9/16)}, preferably less than xe2x85x9c, of the diameter of the hollow fiber bundle.
It is especially advantageous if the channel is circular, i.e., circumferential. Thus, not only a semicircular design of the channel is conceivable, but also a complete circulation.
In another embodiment of the present invention, guide elements are provided in the areas adjacent to the essentially circular or semicircular channel, so that the direction of flow of the fluid leaving the channel can be influenced by these guide elements.
The guide elements may be designed as curved ribs. This makes it possible to distribute the fluid, in particular the blood, uniformly and in a defined manner. This may lead to the development of a small central vortex, but it always has radial symmetry.
It is especially advantageous if the ribs are equidistant in the circumferential direction of the channel. In addition, any other desired arrangement of ribs and guide elements is also conceivable.
The hollow fiber bundle may be held in a tubular casing, with a second flow space being formed through the interior of the casing surrounding the hollow fiber bundle, and with the inflow or outflow chamber being arranged in an end cap connected to the casing at the end. End caps may be provided in both end areas of the casing.
According to a preferred embodiment of the present invention, the hollow fiber bundle extends over the entire cross-sectional area of the casing. It is also conceivable for only partial areas of the cross-sectional area of the casing or the casting compound to be provided with hollow fibers.
It is especially advantageous if each of the end caps has two connections, one of which is connected to the first flow space and the other to the second flow space. Thus, an inlet and an outlet are created for each of the flow spaces, which permits continuous flow through both flow spaces accordingly. The assignment as an inlet or outlet is not fixed, because the connections can be exchanged as needed.
In another embodiment of the present invention, the connections are arranged radially. This applies accordingly for the blood side as well as for the connection for the dialysis solution, which is usually carried through the second flow space. The radial arrangement of the connections may have hydrodynamic advantages. In addition, the arrangement of the connections may also be predetermined by the tube system to be used or by the mounting of the filter device.
According to a preferred embodiment of the present invention, the center lines of the connections run parallel to one another. It is also possible for the center lines of the connections not to pass through the mid point of the end cap.
The mouths of the connections may lie in one plane or in parallel planes. The corresponding design depends essentially on the mount holding the filter device, which should permit rapid and reliable replacement of the filter devices. In another embodiment of the present invention, the connections point in opposite directions.
It is especially advantageous if the casing and the end caps are designed as injection molded parts. This guarantees a reliably simple manufacture, with numerous different embodiments being conceivable.
The present invention also concerns an end cap for a filter device according to the present invention having an inflow or outflow chamber adjacent to an essentially circular or semicircular channel, which is designed to be open in the direction of the ends of the hollow fibers of a hollow fiber bundle arranged in a filter device casing that can be connected to the end cap, and being connected to an inlet or outlet of the end cap, arranged approximately centrically to the hollow fiber bundle and having a cross-sectional area that decreases in the direction of flow, and which has an outside diameter which is less than the inside diameter of the area of the end cap accommodating the hollow fiber bundle.
Advantageous embodiments of the end cap are presented by the embodiments according to the claims.
Additional details and advantages of the present invention are explained in greater detail below on the basis of one embodiment illustrated in the figures.